Transistor tester

[steven2]

dazza ive posted other tesor units before, allso includeing the logic ic tester, check it out

 

[steeve1]

hello
i have built the transistor tester , and it work , i've followed the
revised schematic .

if anyone want it , i have made a pcb with expressPCB

here's the file

 

[MP1]

It is a shame that you made it in ExpressPCB. No one will be able to make the board except ExpressPCB. Do you have them make all your boards or is there a trick to getting it to print out a board pattern so that you can make your own?
BTW- Your file did not attach.

MP

 

[audioguru2]

C'mon Steeve,
Post the pcb so we can get the project corrected (its 4027 still has its clock pin grounded) and nicely completed.
http://www.electronics-lab.com/projects/test/008/index.html

 

[giroup01]

My first project from this board! Works great! Built Manhattan style. Sorry for the poor picture quality though...

View attachment 38461

View attachment 38462

 

[steveco1]

Hi all. As you can see this is my first post having stumbled across this site just recently. I am a relative newby to electronics as well and need some help with this tester. I had all the discussed problems ( 1 LED on all the time etc.) but this was completely solved by the changes given by audioguru. My problem now is that the circuit will identify an NPN or PNP tranny, but will not show whether shorted or open - on a confirmed shorted NPN tranny, the NPN LED still just flashes. Anyone have any idea if I have maybe damaged the 4027, or is this another fault in the circuit? Your feed  back will be very much  appreciated.
Steve.

 

[audioguru2]

Hi Steve,
If the tested transistor is shorted from collector to emitter, then two diodes in series will be across each LED. Two diodes limits the voltage to 1.3V but a LED needs 1.7V or more to light so the LEDs will not light.

If the tested transistor is open then the LEDs will flash like it is not there.

 

[steven2]

the 2 leds will flash if you have no transister being tested hooked up to it and if you do and they flash then  the base and emmitter is shorted out on the transister you are testing

 

[steveco1]

Audioguru, steven thank you for your replies. I have exactly the results as you both describe if I physically dead short the legs - but I have a tranny that measures as follows with a multimeter:
NPN Tranny :B-E = .708V    B-C = .709  C-E one way = .5V    C-E the other  way = clear, B-C reverse polarity = 1.05V.  Surely B to C should only read one way? If I test this tranny in the tranny tester it behaves as if the tranny is good! Why is that?

 

[steven2]

if you are looking at the tran sistor testor i posted some time ago in the forums somewhere it operates by shorting out the  leds or something like that , im no exspert in the technicle exsplanations thing but biuld it, if it works its good enougth

 

[steveco1]

Can anybody help me with the above question? Is the tester maybe not 'sensitive' enough to detect a partial short as in my example?

 

[steven2]

its easy for a short to be tested as a short but for partial shorts ive never herd of a partial short

 

[audioguru2]

The transistor tester circuit is too simple to make a detailed test. It doesn't even test the current gain of the transistors.

 

[steveco1]

Hey I said I'm a newby - I don't know how to explain a leaky transistor between base and collector other than as a partial short. Anyhow, my real question has still not been answered - does anybody who has built this tester know if it does indicate whether a tranny is leaky or have I done something wrong with mine. As I said earlier, if I dead short the tranny at the legs it performs as indicated on the circuit diagram description - but with this transistor reading both ways between base and collector it doesn't pick it up. I know its not that important guys - but I'm trying to learn.
Any suggestions?
Steve.

 

[steven2]

sorey my transistor testor only tells shorts  thats all and thats all i need to know